solar

[donkey]

I am hoping people can correct my errors on the following information in the hope of getting a better knowledge

So far I know the basics. in all systems it is best to have 3 parts. the panels, the battery and a charge controller. So far my research suggests that a 1:1:1/4 ratio is needed that is a 300watt panel for a 300ah battery for a 75 watt load (in perfect conditions of course.)

But this varies if you wish to use the solar for longer or shorter periods of time and daylight hours, and of course if you want to upgrade the load.

If you wish to connect an inverter or use the mains to assist in charging I reccomend a qualified tradesman.

for smaller projects you can use solar panels connect to a diode to the batteries to limit backflow which will drain the batteries if the solar panels are not getting enough sun, In the case of powering up car batteries(or deep cycle batteries which are much more preferable) the charge controller acts as the diode as well as stopping overcharge and over discharge.

A decent charge controller will also have a temperature sensor as different temperatures affect how much the battery can store.

So far I have not found ANY inverter that endorses the use of refrigeration units like fridges, freezers or air conditioning units, as the "kick-in" current can destroy both the inverter and battery.

also I have found our local electrical supplier is not overly happy when people put in solar thinking they are helping. in actual fact the most power produced is outside the peak hours and thus is mostly wasted. most people don't have a battery bank that allows the grid to be fed power when it is needed the most which is typically 6p.m. - 8p.m.

PLEASE PLEASE PLEASE tell me more if there is anything
I would especially like to know the charge controller ratio. like what would be the maximum solar panel to battery ratio a 30amp controller could handle?
Also if I connect an inverter to the system will a 75watt inverter be good for the above setup? or would I need a bigger battery as the inverter would use up some power in the conversion?

 

[Mongrel Shark]

30A controller can handle 30A of panel with any battery, unless controller specs state an amp hour limit or something. Most of them can output the same amount as in, but it's worth checking. Some 20-30 amp controllers don't get along well with inverters........

I connect inverters all the time, But I have been known to zap myself a lot too.... Make sure the inverter is off and you can only zap yourself with battery voltage (normally 12 or 24v). You need someone with an appropriate ticket to grid connect.

nearly all solar panels have diodes on the panel. if not add some! don't trust a controller!


You can run a fridge. BUT! You need about 6 times the watts required to run fridge. So for a 1000w fridge you could use a 2000w with 4000w peak pure sine wave (pure is important with newer fridges) as a bare minimum. Bigger inverter will be more efficient and last longer. I'd recommend something like this r a fridge up to 1500w (ish) Compressors need three time run watts to start! My old 2kw-4kw inverter would not start my air compressor unless tank was open, once it was running I could seal tank, but it would not restart as pressure dropped.... It was not good for compressor or inverter. mostly I used a Genet for compressor... A mate had an inverter to the same spec as in the above link. it started my compressor well. No problems. About the only thing you cant do with an inverter is weld. but you can do that from 24+v dc if your clever..

Choosing battery - panel ratio is tricky. how about telling us more about application and hours of sun available to charge. I had a 200AH battery on less than 10A of panel for a long time. only drawback was it took a few days of good sun to charge it if it got too low. Was a Gel cell though so handled it well. Most batterys will hold more charge and last longer on a slower charge. but if yo need a lot of output you have no choice but to charge hard...

Inverters are around 70% efficient. A rule of thumb I often use is to look at watts of appliance and divide by 10 to get amp drawn from battery. It's not perfect but gets close for most appliances.

75w inverter seems small. especially when you are talking about fridges.I don't like to run inverters at max for long. rarely put more than 1kw of load on my 2kw-4kw inverter. Although part of the reason was because I got it for $300 from Thailand.... They do seem to lose some efficiency on a log curve over half power too... They are so cheap now. might as well get some overkill to be safe..

As far as grid connect power going to waste and being at wrong time... *******s! Power co's don't want to lose you as a customer, and especially don't like the idea of giving you a check. I've worked in big power plants (as a concreter) and I know they have state o the art monitoring kit. They only make whats needed. How would they drain off excess if you made too much? a big system solar will only produce 2kw( you need more inverters to go over that and it get expensive and or complicated). so it's like a very small pee in the ocean... People on your block will probably use that much running all the phone chargers they left plugged in after charging...

I would recommend having batterys though, even for grid connect. You can set it up so you charge the batterys first then dump the excess into the grid... If your good with your batterys you don't draw from the grid... This way you don't get effected by blackouts easily...

I lived on off grid solar for over 10 years and helped many others set up, and do maintenance and upgrades etc.. So can tell you more once I know more. I can find good stuff for cheap on ebay too... I'm going to dob *steve* in too. He knows a lot and will hopefully correct me if I got something wrong.

 

[(*steve*)]

I'm going to dob *steve* in too.

Me?

I agree with you and I obviously won't argue with your experiences.

All I would say is that the mechanism you should follow is:

1) determine the load.
2) determine the inverter requirements
3) determine the amount of battery storage is required
4) determine the charging system required to support that.

(4) embodies panels and charge controllers as you can't really decide on one without some knowledge of the other.

The note about grid connect is a good one. Presuming your load is constant summer and winter, your batteries and panels are pretty much sized for winter. In summer you will have excess generation and if you can sell it to someone then you are further ahead.

 

[donkey]

well so far the loads are simple, 75w ryobi battery charger. a 25watt soldering iron.
later on maybe a power saw and jigsaw. and a light or 2.
this is more a reference for me when I get of my lazy butt so i can come back and review... oh wait, mongrel your on the goldie.... will just pm you to come to rochedale lmao.
as a side topic plasma tv's are they power hungry? just looking at what I can take of the grid power and convert to 12v where possible. thinking the house lights is a big one... I have 2 teenage girls that have no idea bout the off side of a switch.
also if I connect up what i want to solar is there a way to get a ready made power supply 0-12volts that runs of 12v? most of my experiments are in that range with only a few exceptions.

 

[Mongrel Shark]

Lol Plasmas are very power thirsty. Although I have 22 inch lcd that runs right off 12v, draws an amp, 1.5a if I turn the sound right up. Plasmas have 12+ fans in them that probably draw over an amp.... Look on the back where it says how many watts it draws..

As far as 12v power supply. I just hook stuff straight up to the battery, as long as I think it can handle going up to 14.6v (Gel cell) and down around 10v were my controller would turn everything off. Some things even work better. My cheap pc speakers came with a 1A plug pack, when I hooked them up to 12v lighting line I found they actually like to draw 1.5a on loud bass notes... The lcd worked well, probably has power regulators in it... Speakers get a bit quiet at 10v...

I wish I know then that I could run my 19v laptop off a joule thief like step up circuit. When I was out bush. Would have used the inverter a lot less...

You can do LED lighting for super low watts.... Before LEDS got good, I had incandescent car interior lights and the odd blinker globe where I needed something bright. You can also get very efficient 12v fluros. Had one in my kitchen, and another near the reading chairs...
All that was costing me about 20-40w a room though. switched all the incandescents to LED and could light the whole house at once for under 10w. the size of my smallest incandescent.

A power saw is a big step up from a 75w charger... It will have a brushed motor and you need 3x the watts to start it as is whats written on the case.... go 4x to have some confidence the inverter wont play up... I'd suggest something like this for starters. although it wont run a fridge, kettle, toaster, or plasma amongst other high wattage appliances... Its even close enough to pick up and save $10.90. Although I'd pay that to not go to Boonah lol. If your really keen the 2kw-4kw pure sine wave one's are the go. Make sure it does 240v, not just 220v, as some appliances need 230v min.. Also make sure it does all the watts on one outlet. Seen on 2kw inverter put 1000w out each of 2 power points, and the sinewave was opposite so you couldn't make a two headed extension lead ARRrrggggg! But you get stuff like that when you order from china. Best to do you homework first. If you want to run a fridge and a plasma at the same time, you need more batterys and panels lol.


I have a 12v Fridge that is very good. Made on the Sunshine coast by a company called Evercool. Mine is about 170L with a 12L freezer. uses 3A on economy and 6A on boost. Wont freeze stuff on economy, but will freeze a 4L bottle of water in 3-5 hours on boost. keeps stuff frozen on economy... Mine is over 15 years old. I believe the newer ones are better. They are expensive, but they last well if looked after.


If you want less than 12v for electronics there are tons of ways. Long thin wire. Proper resistors. diodes, step down circuits etc etc.... Depends how many amps you want at a given voltage. I hear you can even hook one of those fangled new potentiometer thingamjigs up the right way and get variable voltage at the turn of a knob...



Make sure you get super thick cable from panels to controller/batterys... line loss is your enemy... Although I have some ideas how to defeat that. It's still just a concept atm...
Another thing to remember is this. Mono-crystaline good. Polly-crystaline bad. Mono's last a lot longer and give of more consistent power... It's worth the extra cost.



If you want me to come out. It'll cost you a box of coopers pale ale per visit. I'm a backyard engineer so all care and zero responsibility. You'll only get about 3 hours work out of me then I get too intoxicated and start zapping stuff and falling off roofs.

 

[donkey]

i have a design for something too that you might be interested in if your right into solar, once again only a concept but may help a heap of people.

and while I am at it i see you mention mono and poly... what is amorphious?

 

[Mongrel Shark]

http://en.wikipedia.org/wiki/Amorphous_solid

Seems to mean really thin.


http://en.wikipedia.org/wiki/Solar_cell

Looking at this page it seems to refer to a few types of panel. Most of them fairly new and un tested. I don't know a lot about them. From what I have heard some can be a lot cheaper and give good performance in cloud/shade. Most of them seem to need more sq meters pew watt. I know some of the film ones don't last a long time.

There is a lot of homework to do there and not a lot of info around..

 

[duke37]

Amorphous means non- crystalline.

 

[donkey]

yeah i get all this slowly. but I wish I could get a calculator made to make this easier lol.
it'd be real cool if it somehow calculated the average hours of sunlight (from both sunrise and sundown, and from how much rain you got for the past year averaged out) to accommodate a pretty accurate calculator... man that would be an android app I'd buy lol

 

[donkey]

ok I got a line on some el cheapo solar stuff, but now I got a few little questions
to make it cheap I am getting the panels, no glass protection or casing. so I will make these myself. the question becomes what voltage should I aim for? alot of places I see go up to 18volts... is that too much?
If I get 120 watts out of the panels (making 2 of them) what size battery and charge controller is recommended?
at this point I am thinking about a few LED's to start saving money so won't need much above 120 watts I think. also Briz is getting a heap of rain lately so am factoring that in to the equation too
http://www.ebay.com.au/itm/50-3x6-S.../320721861876?pt=AU_Solar&hash=item4aac833cf4
http://www.ebay.com.au/itm/50-Short.../320721839222?pt=AU_Solar&hash=item4aac82e476
are the products I am considering, but still looking for advice

 

[(*steve*)]

YWIMC!

These are not the magic eqquivalent full sun hours, but from a rough guestimate, you could take about 50% of these figures and use that as a guide. i.e. if the graph says 10 hours of sunlight, then assume your installation will have the equivalent of 5 hours at full power.

Note that it doesn't take into account the affect of cloudy days.

 

[donkey]

ok so what size battery would 120w panels charge over the course of a day and then what size would they charge over 5 days?
am hoping someone can give me the formula so I can figure it out for myself from now on

 

[(*steve*)]

You start out with the equivalent full hours of sun. Let''s say you get 4 hours in winter.

So with 120W of panels (say) you'll get (say) 100W x 4 per day -- 400Wh. That's probably enough to put 300Wh of charge into your batteries. so that gives you 300Wh/day to consume, or about a constant load of 12W

And there you have it. with this particular setup, you need panels rated at about 10 times your average load, and clearly you need battery capacity to suit. (remember that you don't want to discharge the batteries too far, so allow for double the capacity.

This doesn't allow for days that are cloudy If you want to allow for them, maybe you need to add 50% more to your panels and upgrade the battery capacity to allow for x days of load.

Let's say your average load is 1kW (that's about what mine is) I would need 15,000W of panels on the roof and about 150kWh of energy capacity in batteries (that;s about 12500 Ah, or about 1800 of those 7Ah batteries) for 3 days capacity (allows for 2 consecutive cloudy days)

At this point you would stop being so profligate with power.

 

[donkey]

i got watt thingy sorted, but what about battery. they are rated in amp hours panels are in watts.
if I supply 120 watts to a battery for 2 hours (hypothetically a flat 7amp hour battery, although going below 75% is not my intention) how "full" would the battery be?
this is the part that is not easy for me to figure out as people go into the big and small... I just want to know perfect world scenario. x watts= y amp hours

 

[BobK]

For a 12V battery: x Watt Hours = x / 12 Amp Hours.

If you charge a 12V battery with 120W for 2 Hours you will add 10Ah to it, in theory. Of course the efficiency will be less than100% so, probably about 7Ah.

Bob

 

[donkey]

wait my maths seems different to yours.... mine is watts/12volts = amp hours
120 watts/ 12 volts =10 ah
so over 2 hours its 20 ah ... you say 10 ah.... how did you get that for 2 hours?

 

[BobK]

Sorry, my math was wrong, i missed the 2 hours. You are correct, it is 20Ah.

Bob

 

[Mongrel Shark]

You Don't want to put 20ah into a 7ah battery either..

A good charge controller will stop it overcharging, but it dumps the excess as heat (Unless you have a grid connect inverter that kicks in). This is ultimately wasting a little of your panels life. They can only handle so long in the sun and they die. Personally I like to try and use as much of the potential power as possible. Say you have a 10A fuse in your controller, The 120w of panel is right on the limit... You don't want to run in that zone for long... It's just asking for something to go wrong.


Bear in mind there are other ways to store power too. I used to turn the 12v fridge up (from 3A mode to 6Aboost mode)when the batterys where full, Freeze some big bottles of water. This way I have Thermal mass in my fridge at night, and it hardly needs to kick in the compressor.

Another plan I never implemented was to have the controller start a 12v pump when the excess reached a certain point (Enough to run the pump) and pump water into the header tank that gravity fed the house..

I will make these myself. the question becomes what voltage should I aim for? alot of places I see go up to 18volts... is that too much?

Thats about right. Although if you plan on having a long lead (over 10m) from panel to controller/batterys, then you may want to consider going a little higher.. Some panels only make 15v, most seem to be around 17-18v, this seems to supply the battery well.. Perhaps you could make it so you can make small changes ass needed?


The other way you could go a further distance is if you change the DC from the panel to AC, send it to the controller, then turn it back to dc before it enters the controller. There would be some losses in this though, so you'd have to look at how long you charge line in carefully. On that note, can anyone tell me how pulsed dc travels over distance compared to AC and regular flat dc?



As for battery storage. 2 days use with no charge is about the smallest you want to go. I had a weeks storage in my old house, but that has a drawback in that when the sun does come back out, you spend a day or 3 still on rainy power rations to let the battery recharge... Although I had generator backup, and could run a charger off that, So mostly after 3 days of cloud I'd have a "Generator night" where I could turn everything on and not worry about power till the battery was looking a bit better.

 

[donkey]

thanks shark. I wasn't intending on using a 7ah battery I just wanted an example battery
as i am still debating what I am running I am trying to figure out battery size, and panel size, just wanted the ratio's handy

 

[donkey]

http://www.ebay.com.au/itm/120-Shor.../320721841368?pt=AU_Solar&hash=item4aac82ecd8
http://www.ebay.com.au/itm/30A-12V-.../251103747400?pt=AU_Solar&hash=item3a76f31d48
ok so here is my rough calculations
I use the top one to make 3 18volt panels at 60 watts each
I use the 30 amp controller cos that gives me alot of head room for expanding
now for battery... i was thinking http://www.jaycar.com.au/productView.asp?ID=SB1699
a 12volt 38ah battery..... if I am using for basic LED's and maybe a small inverter to recharge my cordless drill will this all work?

my big issue right now is the 18volt from the panels, I am assuming thats maximum voltage right? alot of the charge controllers I see have a max input of 17volt.

also where the heck should I put fuses on this thing?